Abstract
Mechanical properties of beta titanium alloys strongly depend on the precipitation behavior of alpha, which is controlled by thermo-mechanical treatments. To obtain high strength beta titanium alloys, uniform distribution of fine alpha precipitates is required, and various thermo-mechanical treatments have been developed for this purpose.
This paper discusses strengthening by fine alpha precipitation using a thermo-mechanical process which combinates cold rolling and un-recrystallized heat treatments.
High tensile strength of over 1 700 Mpa can be attained by the thermo-mechanical process combining oveer-aging, cold rolling and aging for 86.4 ks at 723 K. Higher strength can be attained after aging by alpha-beta solution treatment than by beta solution treatment because fine alpha particles precipitate in the aging after the former treatment. It seems that un-recrystallized beta matrix supplies the effective nucleation sites of alpha particles.
Ultra high tensile strength of 1 940 Mpa can be attained through the aging after repeated applications of the cold rolling and recovering process. The microstructure after 723 K aging displayed uniform distribution with very fine alpha precipitates 2-5 nm in thickness.
